1. The Structure of the Normal and Hydronephrotic Upper Urinary Tract.- Structure of the Normal Upper Urinary Tract.- Innervation of the Upper Urinary Tract.- Functional Considerations.- Structure of the Upper Urinary Tract in Idiopathic Hydronephrosis.- Aetiological Considerations in Idiopathic Hydronephrosis.- 2. Urodynamics of the Multicalyceal Upper Urinary Tract.- Functional Activity of the Normal Upper Urinary Tract.- Physiology of the Unobstructed Upper Urinary Tract.- The Experimentally Obstructed Upper Urinary Tract.- Functional Activity of the Upper Urinary Tract in Idiopathic Hydronephrosis.- Summary of the Physiology of the Hydronephrotic Upper Urinary Tract.- 3. The Intravenous Urogram in Idiopathic Hydronephrosis.- Acute and Chronic Obstruction.- Normal and Abnormal Standard IVUs.- Clinical Judgement and the Standard IVU.- IVU Modifications.- Conclusions.- 4. Nuclear Medicine.- Parenchymal Transit Time Studies.- Diuresis Renography.- Comparison of Parenchymal Mean Transit Time with Diuresis Renography.- 5. Pressure Flow Studies I.- Clinical Application.- Technique.- Complications.- Interpretation of Results.- Indications in Equivocal Hydronephrosis.- Results of Pressure flow Measurement.- Summary.- 6. Pressure Flow Studies II.- Technique.- Interpretation.- Contraindications.- Conclusions.- 7. Experimental Validation of Diagnostic Methods.- Materials and Methods.- Results.- Discussion.- 8. Idiopathic Hydronephrosis in Children.- Morphological Anomalies.- The Renal Parenchyma.- The Opposite Kidney: Other Congenital Anomalies.- Secondary Pelviureteric Obstruction.- Complications.- Clinical Features.- Treatment.- Results.- 9. The Role of Percutaneous Nephrostomy.- Technique.- Materials.- Renal Drainage.- Retroperitoneal Drainage.- Dilatation of Operative PUJ Strictures.- Stone Dissolution.- Stone Extraction.- Complications.- Summary.- 10. Clinical Management.- Clinical Material.- Discussion.